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I'd like to be able to schedule a server reboot at a specific time, but not regularly. How can I do this without futzing with adding and removing cron entries?

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4 Answers 4

up vote 25 down vote accepted

If it is one-time deal, you can use shutdown command with -r as argument. Instead of using shutdown now, you can add time as parameter (e.g. shutdown -r 12:30).

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6  
For rebooting the -r flag is needed (e.g. shutdown -r 12:30) –  esc1729 Aug 22 '09 at 21:49
2  
-r is critical otherwise you will be hitting a power button somewhere to bring it back up. –  egorgry Aug 22 '09 at 21:51
    
This is true, I forgot -r in initial answer. :( sorry. –  Josip Medved Aug 23 '09 at 18:52
    
This also works with times in the early morning - so if it's 15:55 now, you can use 'shutdown -r 03:15 &' to reboot the server at 3:15am tomorrow morning. (the '&' shunts the command the background so you can log-off without killing the shutdown command) –  Andrew Aug 25 '09 at 14:55
    
This has the advantage/drawback (depending on your use case) of alerting everyone every hour or so via a broadcast message of the upcoming reboot. –  Klaas van Schelven Aug 5 at 8:33

According to the man page: /sbin/shutdown [-t sec] [-arkhncfFHP] time [warning-message] found at --> http://unixhelp.ed.ac.uk/CGI/man-cgi?shutdown+8

Load of options to choose from but, to answer your question.

To reboot in 5 minutes: /sbin/shutdown -r 5 "reboot in five minutes"

To reboot at exactly 11:00 P.M.: /sbin/shutdown -r 23:00 "rebooting at 11:00 P.M."

NOTE: your message will be broadcast to all active terminals / sessions.

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the at command is what you want.

at 5:00pm 
do
cd /
/full/path/to/init 6
done

at -l will list the at cmds

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2  
I would use shutdown instead of init. It's not necessary to do the cd or the do/done (which would probably produce an error). –  Dennis Williamson Aug 22 '09 at 22:17
    
really? I've used this for over 8 years and I've never has an issue. hpux. solaris, linux 2.2 - 2.6 –  egorgry Aug 22 '09 at 22:47
    
I personally prefer init 6 myself; had intermittent issues with shutdown -r on some platforms in the past –  warren Aug 23 '09 at 2:04

the easiest way I can think of is, as root:

sleep 2h && reboot

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